import math
x1,y1,x2,y2=map(float,input().split())

n=(x1-x2)**2+(y1-y2)**2
n1=math.sqrt(n)

print(n1)


 import math math x1,y1,x2,y2=map(float,input().split()) x1 map(float,input().split()) map float input().split() ().split () input split y1 x2 y2 n=(x1-x2)**2+(y1-y2)**2 n (x1-x2)**2+(y1-y2)**2 (x1-x2)**2 x1-x2 x1 x2 2 (y1-y2)**2 y1-y2 y1 y2 2 n1=math.sqrt(n) n1 math.sqrt(n) math.sqrt math sqrt n print(n1) print n1 x1,y1,x2,y2=map(float,input().split()) map(float,input().split()) x1 y1,x2,y2=map(float,input().split()) map(float,input().split()) y1 y2=map(float,input().split()) map(float,input().split()) y2 n1=math.sqrt(n) math.sqrt(n) n1 n=(x1-x2)**2+(y1-y2)**2 (x1-x2)**2+(y1-y2)**2 n x2,y2=map(float,input().split()) map(float,input().split()) x2
import math
x1,y1,x2,y2=map(float,input().split())

n=(x1-x2)**2+(y1-y2)**2
n1=math.sqrt(n)

print(n1)



